With developments in light-emitting diode (LED) technology, lighting solutions that comprise LEDs instead of conventional light bulbs are becoming more popular. An LED comprises a semiconductor diode chip that emits light from an emitter surface. The emitter surface area is very small, usually in a region of only a few square millimeters, sometimes even only a few hundredths of a square millimeter. Such an LED chip can be a top-emitting device, or can emit from the top as well as from the sides. To protect the diode chip, it is usually sealed inside a protective cover, which can also act to improve light extraction. For example, a low-power LED chip inside a transparent plastic or epoxy cover for use as an indicator light of a domestic appliance is generally referred to as “packaged LED”. High-power LED chips such as those used in lighting applications can be mounted directly onto a circuit board, or onto a carrier element that can be connected to a circuit board. The high-power LED chip can be encapsulated or provided with a protective cover that also serves as a filter or other optical element.
A disadvantage of an LED is that the light emitted from the small area of the LED chip is perceived as a small, bright point of light. To make the light source appear larger and less point-like, the light can be spread, for example by an encapsulating dome or a diffusing cover. However, some of the light can be lost in this way, and the overall brightness is diminished. Furthermore, to obtain a large light source for an application such as a brake light, for example, in a prior art arrangement several LED light sources must be arranged over an area corresponding to the area of the desired “light source” in order to provide the necessary luminous flux. However, when several LEDs are arranged thus, the overall impression is one of several distinct bright points of light separated by darker zones. To better achieve the impression of a single light source, such lighting arrangements require diffusers or dedicated lenses to collect, refract and re-combine the light in the desired distribution, whereby such optical elements are always associated with some degree of loss. Furthermore, failure of one of an array of light sources will result in a “hole” in the overall light arrangement.
Since an LED chip emits light according to the Lambert cosine law, the light emitted by the LED is spread essentially evenly in all directions. This is advantageous if a round or circular light source shape is desired. Here, the term “light source shape” refers to the shape of the light source as perceived by an observer, e.g. the shape of a cover of the lighting arrangement containing the LED light source. However, owing to the nature of the light emission from the LED chip, a light source shape that is not round will exhibit less bright regions towards any “corners” or extremities of the light source shape. Clearly, such an uneven light distribution over the light source shape is unfavourable and even unacceptable for certain lighting applications that require an overall even brightness. Therefore, to obtain a light source shape that is not “round”, the light emitted by an LED chip or packaged LED must be manipulated, for example by a system of collectors, reflectors or light guides in order to obtain the light distribution. However, these manipulations result in losses and in a reduction of the overall light output, so that such arrangements are unfavourably inefficient. Also, these arrangements are complicated, bulky and expensive.
Therefore, it is an object of the invention to provide an improved lighting arrangement that overcomes the problems mentioned above.